The Father…the Son and…the Holy Spirit. Matthew 28:20
Words: From an 11th Century manuscript in the British Museum (O Pater sancte, mitis atque pie). Translated from Latin to English by Alfred E. Alston, Some Liturgical Hymns, 1903. For another translation, see Father Most Holy, Merciful and Tender.
Music: Christe Sanctorum French church tune, Paris Antiphoner, 1681 (🔊 pdf nwc).
If you know where to get a good photo of Alston (head-and-shoulders, at least 200×300 pixels),
Father most holy, merciful, and loving,
Jesus, Redeemer, ever to be worshipped,
Life-giving Spirit, Comforter most gracious,
Three in a wondrous unity unbroken,
One perfect God-head, love that never faileth,
Light of the angels, succor of the needy,
Hope of all living.
All Thy creation serveth its creator;
Thee every creature praiseth without ceasing;
We, too, would sing the psalms of true devotion;
Hear, we beseech Thee.
Lord God almighty, unto Thee be glory,
One in three Persons, over all exalted;
Thine, as is meet, be honor, praise, and blessing,
Now and forever.